The present invention relates to a brake system of the type having slip control and includng a master cylinder to which wheel brakes are connected by way of controllable main valves. These systems also include an auxiliary-pressure supply system having a hydraulic pump, a regulating and pressure-monitoring valve as well as a pressure-compensating and pressure fluid supply reservoir, to which supply system the wheel brakes are connected through electromagnetically actuatable inlet and outlet valves. The outlet valves are closed in their inactive condition and each pair of wheel brakes communicates directly with one inlet valve and one outlet valve. Wheel sensors and an electronic circuitry for determining the wheel rotational behavior and for generating electric braking-pressure control signals for the inlet and outlet valves ar also provided in such systems.
In a known brake system of this type, the master cylinder actuates two brake circuits, to which one pair of the two pair of brakes is respectfully allocated. These two brake circuits are in communication each with one pair of wheel brakes thereof the main valves, which are opened in their unactuated condition, and through the inlet valves, which also assume their opened position when in an unactuated condition. The wheel brakes communicate with the pressure-compensating reservoir through the outlet valves, which are closed in their unactuated position, and a hydraulic return line. Also, the two brake circuits are each connected to the auxiliary-pressure supply system, that is, to the hydraulic pump and to the regulating valve by way of a non-return valve and a connecting line. The non-return valves open as soon as the auxiliary pressure rises by a predetermined minimum value in excess of the pressure instantaneously prevailing in the brake circuits between the inlet valves and the main valves. When the hydraulic pump is switched on, the main valves are simultaneously switched over into a second switch position which allows pressure reduction only in the direction toward the master cylinder and the regulating valve. Accordingly, corresponding non-return valves are connected in parallel to the main valves. The non-return valves may be structurally integrated into the main valves.